Lithography system and method for exposing wafer

ABSTRACT

A method is provided. The method includes steps as follows. EUV light is generated. A collector is used to gather the EUV light onto a first optical reflector. The first optical reflector is used to reflect the EUV light to a reticle, so as to impart the EUV light with a pattern. A second optical reflector is used to reflect the EUV light with the pattern onto a wafer. The first optical reflector is rotated.

PRIORITY CLAIM AND CROSS-REFERENCE

This application claims priority to U.S. Provisional Application Ser.No. 62/718,938, filed Aug. 14, 2018, which is herein incorporated byreference.

BACKGROUND

Manufacturing of an integrated circuit (IC) has been driven byincreasing the density of the IC formed in a semiconductor device. Thisis accomplished by implementing more aggressive design rules to allow alarger density of the IC device to be formed. Nonetheless, the increaseddensity of IC devices, such as transistors, has also increased thecomplexity of processing semiconductor devices with decreased featuresizes.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may b e arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 illustrates a lithography system according to some embodiments ofthe present disclosure;

FIG. 2 which illustrates a side view of the optical reflector of FIG. 1;

FIG. 3 illustrates a front view of the optical reflector of FIG. 1;

FIG. 4 is a flow chart of a process according to some embodiments of thepresent disclosure;

FIGS. 5-9 illustrate the lithography system of FIG. 1 with which theprocess of FIG. 4 is implemented at various stages according to someembodiments of the present disclosure;

FIG. 10 is a flow chart of a process according to some embodiments ofthe present disclosure;

FIGS. 11-13 illustrate the lithography system of FIG. 1 with which theprocess of FIG. 10 is implemented according to some embodiments of thepresent disclosure;

FIG. 14 is a flow chart of a process according to some embodiments ofthe present disclosure; and

FIGS. 15-17 illustrate the lithography system of FIG. 1 with which theprocess of FIG. 14 is implemented according to some embodiments of thepresent disclosure.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Furthermore, spatially relative terms, such as “beneath,” “below,”“lower,” “above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

The advanced lithography process, method, and materials described in thecurrent disclosure can be used in many applications, including fin-typefield effect transistors (FinFETs). For example, the fins may bepatterned to produce a relatively close spacing between features, forwhich the above disclosure is well suited. In addition, spacers used informing fins of FinFETs can be processed according to the abovedisclosure.

FIG. 1 illustrates a lithography system 100 according to someembodiments of the present disclosure. The lithography system 100includes a chamber 102, a collector 110, a laser generator 120, adroplet generator 130, a droplet catcher 132, an inlet port 140, anoutlet port 142, optical reflectors 152, 154, 156, 158, 160, 162, 164,166, 168, a reticle 170, a plurality of holders 180, a plurality ofshafts 182, and controllers 190, 192. The lithography system 100 is anextreme ultraviolet (EUV) exposure tool that can perform an exposureoperation for exposing a photoresist layer 302 coated on a wafer 300within the chamber 102. For example, the lithography system 100 mayinclude a stepper 104 disposed within the chamber 102, and the wafer 300on which the photoresist layer 302 is coated is mounted on the stepper104. The stepper 104 is movable in the chamber 102 and is configured toshift the wafer 300, such that the wafer 300 can be shifted at asuitable position for the exposing.

The collector 110 is disposed within the chamber 102. In someembodiments, the collector 110 is mounted to a support (not shown inFIG. 1) that is a part of the lithography system 100. The collector 110has a concave mirror surface 112. The concave mirror surface 112 ofcollector 110 may have a focal point 114 and an axis of symmetry 116which can serve as an optical axis of the collector 110. In greaterdetail, the axis of symmetry 116 of the collector 110 connects a center118 of the mirror surface 112 and the focal point 114.

In some embodiments, the mirror surface 112 of the collector 110 canalso be a multilayer reflector of any suitable structure andcomposition. The mirror surface 112 can include a distributed Braggreflector formed from alternating layers of a high index of refractionmaterial and a low index of refraction material. For example, thealternating layers can be Mo and Si or Mo and Be. In some embodiments,the mirror surface 112 includes more than 20 pairs of alternatinglayers. In some embodiments, the mirror surface 112 obtains areflectivity greater than 60%. In some embodiments, the uppermost layerof the mirror surface 112 can be protected from oxidation by a cappinglayer, such as a layer of Ru. In some embodiments, the mirror surface112 has an opening 113 through the center 118 of the mirror surface 112,and the opening 113 can be provided to allow passage of a light beampropagated from a back side of the collector 110.

The laser generator 120 is disposed within the chamber 102 and at theback side of the collector 110, and thus the mirror surface 112 of thecollector 110 faces away from the laser generator 120. The lasergenerator 120 can be oriented such that the laser beam emitted from thelaser generator 120 can go along the axis of symmetry 116 of the mirrorsurface 112. Stated differently, the laser generator 120 is orientedsuch that an optical path 121 of the laser generator 120 is the same asthe axis of symmetry 116 of the mirror surface 112. The laser generator120 is configured to generate a laser beam aiming at a target 122 infront of the mirror surface 112 of the collector 110. In someembodiments, the target 122 may be between the center 118 and the focalpoint 114 of the mirror surface 112. The laser generator 120 may emit alaser beam from the back side to a front side of the collector 110through the opening 113 of the collector 110. In some embodiments, thelaser generator 120 includes a laser source, such as a pulse carbondioxide (CO₂) laser source.

The droplet generator 130 and the droplet catcher 132 are disposedwithin the chamber 102 and on two opposite sides of the collector 110(e.g., a left side and a right side of the collector 110). The dropletgenerator 130 aims at the target 122 and thus shoots droplets along adroplet path 131 to the target 122. The droplet generator 130 isoriented such that the droplet path 131 intersects the axis of symmetry116 of the mirror surface 112 at the target 122. Because the opticalpath 121 of the laser generator 120 is the same as the axis of symmetry116 of the mirror surface 112, the droplet path 131 intersects theoptical path 121 of the laser generator 120 as well. The droplet catcher132 is configured to catch the droplets from the droplet generator 130.In some embodiments, example materials shot from the droplet generator130 may include tin or other suitable material that can be used togenerate EUV. In some embodiments, the pulses of the laser beam providedby the laser generator 120 and the droplet generating rate of thedroplet generator 130 are controlled to be synchronized such that thedroplets receive peak powers consistently from the laser pulses of thelaser beam. In some embodiments, the laser generator 120 and the dropletgenerator 130 can be collectively operated to generate EUV light, andtherefore the laser generator 120 in combination with the dropletgenerator 130 can serve as an EUV light source.

The inlet port 140 and the outlet port 142 pass sidewalls of the chamber102 and are coupled to the inside of the chamber 102. In someembodiments, the inlet port 140 and the outlet port 142 are configuredto provide a gas flow through the chamber 102 during the operation ofthe lithography system 100, so as to protect the collector 110 fromcontaminations, such as tin particles (e.g., tin debris).

The optical reflectors 152, 154, 156, 158, 160, 162, 164, 166, 168 arewithin the chamber 102. The optical reflectors 152, 154, 156 areoptically coupled between the collector 110 and the reticle 170, and theoptical reflectors 158, 160, 162, 164, 166, and 168 are opticallycoupled between the reticle 170 and the photoresist layer 302 on thewafer 300. The optical reflector 152 is optically coupled to thecollector 110, and thus the mirror surface 112 of the collector 110 canreflect a light beam to the optical reflector 152. Afterward, the lightbeam can be reflected from the optical reflector 152 to the reticle 170through reflection by the optical reflectors 154, 156. The opticalreflector 158 is optically coupled to the reticle 170, and thus thelight beam can be reflected from the reticle 170 to the opticalreflector 158. Thereafter, the light beam can be reflected from theoptical reflector 158 to the photoresist layer 302 through reflection bythe optical reflectors 160, 162, 164, 166, and 168.

In some embodiments, the optical reflectors 152, 154, 156, 158, 160,162, 164, 166, 168 are mirrors which respectively have reflectionsurfaces. In some embodiments, the optical reflectors 152, 154, 156, 158can be multilayer structures that operate as distributed Braggsreflectors. The thickness of the layers can be optimized for each of theoptical reflectors 152, 154, 156, 158 with respect to wavelength andangle of an incident light beam. In some embodiments, a first group ofthe optical reflectors 152, 154, 156, 158, 160, 162, 164, 166, 168includes at least one concave mirror, and a second group of the opticalreflectors 152, 154, 156, 158, 160, 162, 164, 166, 168 includes at leastone convex mirror.

In some embodiments, a light beam propagated from the collector 110 tothe optical reflectors 152, 154, 156, 158, 160, 162, 164, 166, 168 is anoff-axis light beam with respect to the optical reflectors 152, 154,156, 158, 160, 162, 164, 166, 168. For example, the optical reflector152 has a center 152C, an annular edge 152E, and a non-central zone 152Zbetween the center 152C and the annular edge 152E, and the collector 110and the optical reflector 152 are oriented such that a light beamreflected from the collector 110 can be incident on the non-central zone152Z of the optical reflector 152. In this way, the light beam is offsetfrom the center 152C and thus referred to as an off-axis light beam withrespect to the optical reflector 152. In some embodiments, the axis ofsymmetry 116 of the collector 110 intersects the non-central zone 152Z,not the center 152C of the optical reflector 152, which in turn will behelpful for directing the light beam to the non-central zone 152Z.

In some embodiments, the optical reflectors 152, 154, 156, 158, 160,162, 164, 166, 168 are respectively mounted to the holders 180 withinthe chamber 102, and the holders 180 are mounted to the correspondingshafts 182 within the chamber 102. In some embodiments, the holders 180are rotatably mounted to the corresponding shafts 182, and suchrotatable mounting can be any mounting system that connects the holders180 and permits optical reflectors 152, 154, 156, 158, 160, 162, 164,166, 168 to be rotated (i.e., revolved) without detaching it from itsmounting.

For example, as shown in FIG. 2 which illustrates a side view of theoptical reflector 152 of FIG. 1, the lithography system 100 furtherincludes a motor 184 coupled to the shaft 182 and configured to drivethe shaft 182 to rotate. In some embodiments, the motor 184 includes amicro electro mechanical system (MEMS) motor, a piezoelectric (PZT)motor, a DC (direct current) motor, or combinations thereof. In someembodiments, the optical reflector 152 is stably mounted to the holder180, and the holder 180 is stably mounted to shaft 182. As such, theoptical reflector 152 is mechanically connected to the motor 184. Inthis way, the optical reflector 152 can be rotated. For example, whenthe shaft 182 is driven by the motor 184 to rotate, the holder 180 andthe optical reflector 152 are thus rotated. In some embodiments, theoptical reflector 152 has an axis of symmetry 153 aligned with an axisof symmetry 183 of the shaft 182. In this way, when the shaft 182 isdriven by the motor 184 to rotate about the axis of symmetry 183, theholder 180 and the optical reflector 152 thereon can rotate about theaxis of symmetry 153.

The holder 180 has a front surface 180F facing the optical reflector 152and a back surface 180B facing away from the optical reflector 152. Insome embodiments, the front surface 180F of the holder 180 is concaveand conformal to a back surface 152B of the optical reflector 152 facingthe holder 180. In the example configuration in FIG. 2, the back surface180B of the holder 180 is a substantially flat surface. In otherembodiments, the back surface 180B of the holder 180 is a curvedsurface. In some embodiments, the shaft 182 is fixed to the back surface180B of the holder 180 to secure the holder 180.

FIG. 3 illustrates a front view of the optical reflector 152 of FIG. 1.As shown in FIGS. 2 and 3, in some embodiments, the annular edge 152E ofthe optical reflector 152 is fixed to the holder 180. In someembodiments, the lithography system 100 further includes a plurality ofrollers 186 to assist with the rotation of the optical reflector 152.The rollers 186 are arranged to be in contact with a perimeter of theholder 180. Such arrangement can be referred to as a perimeter mounting,which in turn will be advantageous for high positional stability.

Reference is made back to FIG. 1. The reticle 170 can be used to impartthe light beam with a pattern so as to create a pattern in thephotoresist layer 302 and thus the wafer 300. It is noted that thepattern imparted to the light beam may not exactly correspond to thedesired pattern in the wafer, for example if the pattern includesphase-shifting features. Generally, the pattern imparted to the lightbeam will correspond to a particular functional layer in a device beingcreated in the wafer, such as an integrated circuit. In someembodiments, the reticle 170 may include a distributed Bragg reflector.In some embodiments, the reticle 170 may include phase shifting layersand/or absorber layers to define the pattern. In some embodiments, thereticle 170 is an absorberless phase-shifting mask.

The controllers 190A, 190B, 190C, 190D, 190E, 190F, 190G, 190H, 190I(collectively, the controller 190) are respectively electricallyconnected to the motors (e.g., the motor 184 of FIG. 2) which areconfigured to rotate the respective optical reflectors 152, 154, 156,158, 160, 162, 164, 166, 168. In some embodiments, the controllers190A-190I can be configured to determine whether to drive the rotationof the corresponding optical reflector (e.g., the optical reflector 152,154, 156, 158, 160, 162, 164, 166, or 168). In some embodiments, thecontroller 192 is electrically connected to the laser generator 120 andthe droplet generator 130 and is configured to trigger the laseremission operation of the laser generator 120 and the droplet shootingoperation of the droplet generator 130.

In some embodiments, the controllers 190A-190I and 192 can be programmedsuch that the controllers 190A-190I can trigger rotations of thecorresponding optical reflector (e.g., the optical reflector 152, 154,156, 158, 160, 162, 164, 166, or 168) before the controller 192 triggersthe laser emission operation and the droplet shooting operation. In someembodiments, the controllers 190A-190I and 192 can be programmed suchthat the controllers 190A-190I can trigger rotations of thecorresponding optical reflector (e.g., the optical reflector 152, 154,156, 158, 160, 162, 164, 166, or 168) after the controller 192 triggersthe laser emission operation and the droplet shooting operation. In someembodiments, the controllers 190A-190I and 192 can be programmed suchthat the controllers 190A-190I can trigger rotations of thecorresponding optical reflector (e.g., the optical reflector 152, 154,156, 158, 160, 162, 164, 166, or 168) before the controller 192 haltsthe laser emission operation and the droplet shooting operation. In someembodiments, the controllers 190A-190I and 192 can be programmed suchthat the controllers 190A-190I can trigger rotations of thecorresponding optical reflector (e.g., the optical reflector 152, 154,156, 158, 160, 162, 164, 166, or 168) after the controller 192 halts thelaser emission operation and the droplet shooting operation.

In some embodiments, the controllers 190A-190I and 192 can be programmedsuch that the controllers 190A-190I can halt rotations of thecorresponding optical reflector (e.g., the optical reflector 152, 154,156, 158, 160, 162, 164, 166, or 168) before the controller 192 haltsthe laser emission operation and the droplet shooting operation. In someembodiments, the controllers 190A-190I and 192 can be programmed suchthat the controllers 190A-190I can halt rotations of the correspondingoptical reflector (e.g., the optical reflector 152, 154, 156, 158, 160,162, 164, 166, or 168) after the controller 192 halts the laser emissionoperation and the droplet shooting operation.

In some embodiments, the rotations, the laser emission operation, andthe droplet shooting operation are controlled to be synchronized, andthe controllers 190A-190I and 192 can be programmed such that thecontrollers 190A-190I can trigger rotations of the corresponding opticalreflector (e.g., the optical reflector 152, 154, 156, 158, 160, 162,164, 166, or 168) during the controller 192 triggers the laser emissionoperation and the droplet shooting operation. For example, thecontrollers 190A-190I and 192 can be programmed such that thecontrollers 190A-190I triggers rotations of the corresponding opticalreflector (e.g., the optical reflector 152, 154, 156, 158, 160, 162,164, 166, or 168) and the controller 192 triggers the laser emissionoperation and the droplet shooting operation at the same time.

In some embodiments, after halting the laser emission operation and thedroplet shooting operation, the controller 192 can be programmed toresume the laser emission operation and the droplet shooting operation.In some embodiments, after halting the rotations of the correspondingoptical reflector (e.g., the optical reflector 152, 154, 156, 158, 160,162, 164, 166, or 168), the controllers 190A-190I can be programmed toresume the corresponding rotations.

FIG. 4 is a flow chart of a process 200 according to some embodiments ofthe present disclosure. FIGS. 5-9 illustrate the lithography system 100of FIG. 1 with which the process 200 of FIG. 4 is implemented at variousstages according to some embodiments of the present disclosure. Theprocess 200 includes actions S210, S220, S230, S240, and S250. Thelithography system 100 can be operated to expose a photoresist layercoated on a wafer by the process 200. For example, as shown in FIG. 5,the wafer 300 on which the photoresist layer 302 is coated is mounted onthe stepper 104 within the chamber 102, and the lithography system 100is operated to expose the photoresist layer 302 coated on the wafer 300.

The action S210 is generating a laser beam from a laser generator. Forexample, as shown in FIG. 5, the controller 192 can be programmed totrigger a laser emission operation such that the laser generator 120 cangenerate a laser beam 310. As previously described, the laser generator120 can be oriented such that the laser beam 310 emitted from the lasergenerator 120 can go along the axis of symmetry 116 of the mirrorsurface 112, and the laser generator 120 is configured to generate thelaser beam 310 aiming at the target 122 in front of the mirror surface112 of the collector 110. As such, the laser beam 310 can be sent to thetarget 122 in the axis of symmetry 116 of the mirror surface 112.

The action S220 is generating droplets by a droplet generator. Forexample, as shown in FIG. 5, the controller 192 can be programmed totrigger a droplet shooting operation such that droplets 312 aregenerated by the droplet generator 130. In some embodiments, thedroplets 312 may include tin or other suitable materials that can beused to generate EUV. In some embodiments, the droplets 312 from thedroplet generator 130 may be caught by the droplet catcher 132. Sincethe droplet generator 130 aims at the target 122, the droplets 312 canbe directed to the target 122 by the droplet generator 130 such that thelaser beam 310 is incident on a droplet 312T.

Thereafter, the droplet 312T can be irradiated by the laser beam 310, soas to produce high-temperature plasma 314 by heating the droplet 312T.In some embodiments, the high-temperature plasma 314 may be referred toas a microplasma which can generate EUV light 316. In some embodiments,the lithography system 100 produces EUV light 316 with a wavelength inthe range from 3 nm to 15 nm, for example a wavelength of about 13.5 nm.A generator for droplets other than tin can be used in place of thedroplet generator 130 and another wavelength laser can replace the lasergenerator 120, and the microplasma can be formed in any suitable manner.In some embodiments, the controller 192 can be programmed to trigger thelaser emission operation and the droplet shooting operation, and the EUVlight 316 is generated in response to the laser emission operation andthe droplet shooting operation.

The EUV light 316 is reflected by the mirror surface 112 of thecollector 110 toward the optical reflector 152. In some embodiments, theEUV light 316 is widely scattered to produce the reflected EUV light.The collector 110 can gather the EUV light 316 and direct the EUV light316 onto the optical reflector 152. The EUV light 316 then can bereflected by the optical reflectors 152, 154, 156 in sequence and to thereticle 170 as illustrated in FIG. 5. The reticle 170 reflects the EUVlight 316, which in turn imparts the EUV light 316 with a pattern.

Reference is made to FIGS. 5 and 6, in which FIG. 6 is a front view ofthe optical reflector 152 of FIG. 5. The collector 110 and the opticalreflector 152 are oriented such that the EUV light 316 reflected fromthe collector 110 can be incident on the non-central zone 152Z of theoptical reflector 152. For example, the EUV light 316 may illuminateonto a first region R1 within the non-central zone 152Z of the opticalreflector 152, as shown in FIG. 6. Accordingly, the light beam 310 isoffset from the center 152C and thus referred to as an off-axis EUVlight beam with respect to the optical reflector 152.

After using the optical reflectors 152, 154, 156 to reflect the EUVlight 316 to the reticle 170, a pattern is imparted to the EUV light316. Thereafter, the EUV light 316 imparted with the pattern is directedto the photoresist 302 coated on the wafer 300 by the optical reflectors158, 160, 162, 164, 166, 168. Similarly, the EUV light 316 incident onthe optical reflectors 154, 156, 158, 160, 162, 164, 166, 168 is anoff-axis EUV light beam with respect to the corresponding opticalreflectors 154, 156, 158, 160, 162, 164, 166, 168. The lithographysystem 100 thereby selectively exposes the photoresist 302 coated on thewafer 300 in a pattern defined by the reticle 170 (i.e., the patternimparted to the EUV light 316).

The action S230 is providing a gas flow through a chamber. For example,as shown in FIG. 5, a gas flow 320 is provided to flow through thechamber 102. The gas flow 320 can enter the chamber 102 through theinlet port 140, and the gas flow 320 can leave the chamber 102 throughoutlet port 142. In some embodiments, the gas flow is provided to flowthrough the chamber 102 in which the collector 110 and other componentsof the lithography system 100 are enclosed.

Following the actions S210, S220, and S230, the process 200 continueswith the action S240 which is halting generating the laser beam and thedroplets. For example, as shown in FIG. 7, the controller 192 can beprogrammed to halt the laser emission operation and the droplet shootingoperation, and the generation of the EUV light is halted as well.

Thereafter, the process 200 continues with the action S250 which isrotating at least one of optical reflectors. For example, as shown inFIGS. 8 and 9, the controllers 190A-190I can be programmed to triggerrotations of the optical reflectors 152, 154, 156, 158, 160, 162, 164,166, and 168 such that the optical reflectors 152, 154, 156, 158, 160,162, 164, 166, and 168 are rotated. Stated differently, the controllers190A-190I and 192 can be programmed such that the controllers 190A-190Ican trigger the rotations of the optical reflectors 152, 154, 156, 158,160, 162, 164, 166, or 168 after the controller 192 triggers and haltsthe laser emission operation and the droplet shooting operation.

In some embodiments, the optical reflectors 152, 154, 156, 158, 160,162, 164, 166, or 168 are rotated by applying mechanical force providedby the motors (e.g., the motor 184 of FIG. 2) which are mechanicallyconnected to the optical reflectors 152, 154, 156, 158, 160, 162, 164,166, 168, respectively, through the corresponding shafts 182. In someembodiments, the optical reflectors 152, 154, 156, 158, 160, 162, 164,166, 168 can be rotated about the centers thereof, and the rotatedoptical reflectors 152, 154, 156, 158, 160, 162, 164, 166, 168 are freefrom translation motion during the rotations. For example, the opticalreflector 152 is rotated about the center 152C thereof. In someembodiments, the action S240 further includes rotating at least one ofthe optical reflectors 152, 154, 156, 158, 160, 162, 164, 166, 168 by apredetermined angle in a range from, for example, 1 degree to 359degrees. In some embodiments, the predetermined angle is sufficient tomake at least one of the optical reflectors 152, 154, 156, 158, 160,162, 164, 166, 168 rotate such that a next to-be-illuminated regionnon-overlaps with an unilluminated region. In some embodiments, rotatingat least one of the optical reflectors 152, 154, 156, 158, 160, 162,164, 166, 168 by the predetermined angle can be achieved by thecontrollers 190A-190I. In some embodiments, the optical reflectors 152,154, 156, 158, 160, 162, 164, 166, 168 are rotated by the same angle. Insome embodiments, two of the optical reflectors 152, 154, 156, 158, 160,162, 164, 166, 168 are rotated by different angles. In some embodiments,the optical reflectors 152, 154, 156, 158, 160, 162, 164, 166, 168 arerotated until the controllers 190A-190 halt the rotations of thecorresponding optical reflectors 152, 154, 156, 158, 160, 162, 164, 166,168.

By rotating the optical reflectors 152, 154, 156, 158, 160, 162, 164,166, 168, the illuminated regions of the optical reflectors 152, 154,156, 158, 160, 162, 164, 166, 168 are left from the original positionsthereof, and the unilluminated regions of the optical reflectors 152,154, 156, 158, 160, 162, 164, 166, 168 are rotated to positions the sameas the original positions of the illuminated regions of the opticalreflectors 152, 154, 156, 158, 160, 162, 164, 166, 168. For example, asshown in FIG. 9, with respect to the optical reflector 152, the firstregion R1 within the non-central zone 152Z is the illuminated region,and a second region R2 within the non-central zone 152Z is theunilluminated region. In some embodiments, the optical reflector 152 isrotated by less than one turn. By rotating the optical reflector 152,the first region R1 is left from the original position thereof, and thesecond region R2 is rotated to a position the same as the originalposition of the first region R1. The position of the first region R1with respect to the chamber 102 prior to the rotation may be the same asthe position of the second region R2 with respect to the chamber 102after the rotation. As such, the second region R2 (i.e., a nextto-be-illuminated region) can reflect EUV light instead of the firstregion R1 (i.e., an already-illuminated region). For example, afterrotating the optical reflector 152, the unilluminated regions thereof(e.g., the second region R2) can be configured to reflect EUV light in asubsequent exposure process.

In this regard, during the laser emission operation and the dropletshooting operation, the EUV light (e.g., the EUV light 316 illustratedin FIG. 5) that is incident on the first region R1 would cause adecrease in the reflectivity of the first region R1 as time passes, andthus the second region R2 may therefore have the reflectivity higherthan that of the first region R1 due to reduced EUV light exposure. Byrotating the optical reflectors 152, 154, 156, 158, 160, 162, 164, 166,168, EUV light can be reflected from these “unilluminated regions” ofthe optical reflectors 152, 154, 156, 158, 160, 162, 164, 166, 168during a subsequent exposure process, which can be advantageous foravoiding energy loss of the EUV light which is applied to a photoresistlayer.

In the example configuration in FIGS. 8 and 9, the controllers 190A-190Iare programmed to trigger and halt the rotations of the opticalreflectors 152, 154, 156, 158, 160, 162, 164, 166, 168 after triggeringand halting the laser emission operation and the droplet shootingoperation by the controller 192. In other embodiments, the controllers190A-190I are programmed to trigger and halt the rotations of theoptical reflectors 152, 154, 156, 158, 160, 162, 164, 166, 168 beforetriggering and halting the laser emission operation and the dropletshooting operation by the controller 192.

In the example configuration in FIGS. 8 and 9, the optical reflectors152, 154, 156, 158, 160, 162, 164, 166, 168 are rotated. In otherembodiments, a first group of the optical reflectors 152, 154, 156, 158,160, 162, 164, 166, 168 is rotated, and a second group of the opticalreflectors 152, 154, 156, 158, 160, 162, 164, 166, 168 is static (i.e.,stationary). For example, when the rotation of the optical reflector 152is triggered such that the optical reflector 152 rotates, the opticalreflector 160 may be static.

FIG. 10 is a flow chart of a process 400 according to some embodimentsof the present disclosure. FIGS. 11-13 illustrate the lithography system100 of FIG. 1 with which the process 400 of FIG. 10 is implementedaccording to some embodiments of the present disclosure. The process 400includes actions S410, S420, S430, S440, S450, and S460. The lithographysystem 100 can be operated to expose a photoresist layer coated on awafer by the process 400. For example, as shown in FIG. 11, the wafer300 on which the photoresist layer 302 is coated is mounted on thestepper 104 within the chamber 102, and the lithography system 100 isoperated to expose the photoresist layer 302 coated on the wafer 300.

Many aspects of the process 400 are the same as or similar to those ofthe process 200 as previously described in FIG. 4. For example, theaction S410 is generating a laser beam from a laser generator, and manyaspects of the action S410 are the same as or similar to those of theaction S210 as previously described in FIG. 5. The action S420 isgenerating droplets by a droplet generator, and many aspects of theaction S420 are the same as or similar to those of the action S220 aspreviously described in FIG. 5. The action S430 is providing a gas flowthrough a chamber, and many aspects of the action S430 are the same asor similar to those of the action S230 as previously described in FIG.5. During the actions S410, S420, and S430, EUV light is generated aswell. For example, as shown in FIG. 11, EUV light 316 is generated toexpose the photoresist layer 302 coated on the wafer 300. Because theactions S410, S420, and S430 can be performed as previously described inFIG. 5, and the detailed explanation may be omitted.

Different from the process 200, in the process 400, triggering arotation of at least one of optical reflectors is performed beforehalting the laser emission operation and the droplet shooting operation.Accordingly, following the actions S410, S420, and S430, the process 400continues with the action S440 which is rotating at least one of opticalreflectors. For example, as shown in FIG. 12, the controllers 190A-190Ican be programmed to trigger rotations of the optical reflectors 152,154, 156, 158, 160, 162, 164, 166, 168 while the EUV light 316 isgenerated, such that the optical reflectors 152, 154, 156, 158, 160,162, 164, 166, 168 are rotated during the generation of the EUV light316 (i.e., during the laser emission operation and the droplet shootingoperation).

Thereafter, the process 400 continues with the actions S450 which ishalting rotating at least one of the optical reflectors. For example, asshown in FIG. 13, before the controller 192 halts the laser emissionoperation and the droplet shooting operation, the controllers 190A-190Iand 192 can be programmed such that the controllers 190A-190I can haltthe rotations of the optical reflectors 152, 154, 156, 158, 160, 162,164, 166, 168 and that the optical reflectors 152, 154, 156, 158, 160,162, 164, 166, 168 are static. Stated differently, after halting therotations of the optical reflectors 152, 154, 156, 158, 160, 162, 164,166, 168, the EUV light 316 is generated while the optical reflectors152, 154, 156, 158, 160, 162, 164, 166, 168 are static.

Afterward, the process 400 continues with the action S460 which ishalting generating the laser beam and the droplets. For example, thecontroller 192 can be programmed to halt the laser emission operationand the droplet shooting operation, such that generating the laser beamand the droplets is halted and thus the generation of the EUV light ishalted as well.

In the example configuration in FIG. 13, the controllers 190A-190I areprogrammed to halt the rotations of the optical reflectors 152, 154,156, 158, 160, 162, 164, 166, 168 before halting the laser emissionoperation and the droplet shooting operation by the controller 192. Inother embodiments, the controllers 190A-190I are programmed to halt therotations of the optical reflectors 152, 154, 156, 158, 160, 162, 164,166, 168 after halting the laser emission operation and the dropletshooting operation by the controller 192.

FIG. 14 is a flow chart of a process 500 according to some embodimentsof the present disclosure. FIGS. 15-17 illustrate the lithography system100 of FIG. 1 with which the process 500 of FIG. 14 is implementedaccording to some embodiments of the present disclosure. The process 500includes actions S510, S520, S530, S540, S550, and S560. The lithographysystem 100 can be operated to expose a photoresist layer coated on awafer by the process 500. For example, as shown in FIG. 15, the wafer300 on which the photoresist layer 302 is coated is mounted on thestepper 104 within the chamber 102, and the lithography system 100 isoperated to expose the photoresist layer 302 coated on the wafer 300.

Many aspects of the process 500 are the same as or similar to those ofthe process 200 as previously described in FIG. 4. For example, theaction S520 is generating a laser beam from a laser generator, and manyaspects of the action S520 are the same as or similar to those of theaction S210 as previously described in FIG. 5. The action S530 isgenerating droplets by a droplet generator, and many aspects of theaction S530 are the same as or similar to those of the action S220 aspreviously described in FIG. 5. The action S540 is providing a gas flowthrough a chamber, and many aspects of the action S540 are the same asor similar to those of the action S230 as previously described in FIG.5. During the actions S520, S530, and S540, EUV light is generated aswell. Because the actions S520, S530, and S540 can be performed aspreviously described in FIG. 5, and the detailed explanation may beomitted.

Different from the process 200, in the process 500, triggering arotation of at least one of optical reflectors is performed beforetriggering the laser emission operation and the droplet shootingoperation. Accordingly, prior to the actions S520, S530, and S540, theaction S510 which is rotating at least one of optical reflectors isperformed. For example, as shown in FIG. 15, the controllers 190A-190Ican be programmed to trigger rotations of the optical reflectors 152,154, 156, 158, 160, 162, 164, 166, 168.

Following the action S510, the actions S520, S530, and S540 areperformed, such that EUV light 316 is generated to expose thephotoresist layer 302 coated on the wafer 300, as shown in FIG. 16.during the actions S520, S530, and S540 (i.e., during the laser emissionoperation and the droplet shooting operation), the optical reflectors152, 154, 156, 158, 160, 162, 164, 166, 168 are rotated while the EUVlight 316 is generated. Explained in different ways, the opticalreflectors 152, 154, 156, 158, 160, 162, 164, 166, 168 continuouslyrotate during an entire period of being incident with EUV light 316.

Thereafter, the process 500 continues with the actions S550 which ishalting generating the laser beam and the droplets. For example, asshown in FIG. 17, before the controllers 190A-190I halt the rotations ofthe optical reflectors 152, 154, 156, 158, 160, 162, 164, 166, 168, thecontrollers 190A-190I and 192 can be programmed such that thecontrollers the controller 192 can halt the laser emission operation andthe droplet shooting operation, so as to halt generating the laser beamand the droplets. Stated differently, after halting the laser emissionoperation and the droplet shooting operation, the optical reflectors152, 154, 156, 158, 160, 162, 164, 166, 168 are rotated withoutreflecting EUV light.

Afterward, the process 500 continues with the action S560 which ishalting rotating at least one of the optical reflectors. For example,the controllers 190A-190I can be programmed to halt the rotations of theoptical reflectors 152, 154, 156, 158, 160, 162, 164, 166, 168, suchthat the optical reflectors 152, 154, 156, 158, 160, 162, 164, 166, 168are static.

In the example configuration in FIG. 17, the controller 192 isprogrammed to halt the laser emission operation and the droplet shootingoperation before halting the rotations of the optical reflectors 152,154, 156, 158, 160, 162, 164, 166, 168. In other embodiments, thecontroller 192 is programmed to halt the laser emission operation andthe droplet shooting operation after halting the rotations of theoptical reflectors 152, 154, 156, 158, 160, 162, 164, 166, 168.

Based on the above discussions, it can be seen that the presentdisclosure offers advantages. It is understood, however, that otherembodiments may offer additional advantages, and not all advantages arenecessarily disclosed herein, and that no particular advantage isrequired for all embodiments. One advantage is that the opticalreflectors can be driven to rotate by the corresponding motors, and thusdifferent regions of each of the reflections surfaces of the opticalreflectors can reflect EUV light in different exposing operations, whichin turn will be advantageous for avoiding energy loss of the EUV lightwhich is applied to a photoresist layer. Moreover, since the differentregions of each of the reflections surfaces of the optical reflectorscan reflect EUV light as time passes, it can prevent the EUV light fromfocusing on a specific region of each of the reflections surfaces of theoptical reflectors, which in turn will reduce deterioration andcontamination on the optical reflectors. Accordingly, throughput andyield of the EUV process can be improved. Another advantage is thattriggering and halting the rotations of the optical reflector can beindependent of triggering and halting the laser emission operation andthe droplet shooting operation, which in turn will be advantageous forachieving a flexible process for exposing the wafer.

According to various embodiments of the present disclosure, a method isprovided. The method includes steps as follows. EUV light is generated.A collector is used to gather the EUV light onto a first opticalreflector. The first optical reflector is used to reflect the EUV lightto a reticle, so as to impart the EUV light with a pattern. A secondoptical reflector is used to reflect the EUV light with the pattern ontoa wafer. The first optical reflector is rotated.

According to various embodiments of the present disclosure, a method isprovided. The method includes steps as follows. EUV light is generatedin a chamber. A collector is used to gather the EUV light onto a firstregion of a first optical reflector. The first region of the firstoptical reflector is used to reflect the EUV light to a reticle toimpart the EUV light with a pattern. A second optical reflector is usedto reflect the EUV light with the pattern onto a wafer within thechamber. The first optical reflector is revolved, such that the EUVlight is reflected by a second region of the first optical reflector, inwhich the first region of the first optical reflector is free fromemitted by the EUV light when the EUV light is reflected by the secondregion of the first optical reflector.

According to various embodiments of the present disclosure, anlithography system includes a collector, a laser generator, a dropletgenerator, and a rotatable optical reflector. The collector has a mirrorsurface and an optical axis. The laser generator aims at a position inthe optical axis and in front of the mirror surface. The dropletgenerator aims at the position. The rotatable optical reflector overlapswith the optical axis of the collector.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A method comprising: generating extremeultraviolet (EUV) light, wherein generating the EUV light comprises:generating a laser beam aiming at a target from a laser generator; andshooting at least one droplet at the target from a droplet generator,such that the droplet is illuminated by the laser beam and the EUV lightis generated; using a collector to gather the EUV light onto a firstoptical reflector; using the first optical reflector to reflect the EUVlight to a reticle, so as to impart the EUV light with a pattern; usinga second optical reflector to reflect the EUV light with the patternonto a wafer; and rotating the first optical reflector; halting rotatingthe first optical reflector; and halting generating the laser beam andshooting the droplet after halting rotating the first optical reflector.2. The method of claim 1, wherein rotating the first optical reflectoris performed after generating the laser beam and shooting the droplet.3. The method of claim 1, wherein generating the laser beam and shootingthe droplet are performed after rotating the first optical reflector. 4.The method of claim 1, wherein generating the EUV light is performedduring rotating the first optical reflector.
 5. The method of claim 1,wherein using the first optical reflector to reflect the EUV light isperformed during rotating the first optical reflector.
 6. The method ofclaim 1, further comprising: rotating the second optical reflector suchthat the second optical reflector rotates during rotating the firstoptical reflector.
 7. A method comprising: generating extremeultraviolet (EUV) light in a chamber, wherein generating the EUV lightcomprises: generating a laser beam aiming at a target from a lasergenerator; and shooting at least one droplet at the target from adroplet generator, such that the droplet is illuminate by the laser beamand the EUV light is generated; using a collector to gather the EUVlight onto a first region of a first optical reflector; using the firstregion of the first optical reflector to reflect the EUV light to areticle to impart the EUV light with a pattern; using a second opticalreflector to reflect the EUV light with the pattern onto a wafer withinthe chamber; revolving the first optical reflector, such that the EUVlight is reflected by a second region of the first optical reflector,wherein the first region of the first optical reflector is free fromincidence of the EUV light when the EUV light is reflected by the secondregion of the first optical reflector; halting revolving the firstoptical reflector; and halting generating the laser beam and shootingthe droplet after revolving the first optical reflector.
 8. The methodof claim 7, wherein the EUV light is gathered to the first opticalreflector at a position with respect to the chamber, and the positionoverlaps the first region prior to rotating the first optical reflectorand overlaps the second region after rotating the first opticalreflector.
 9. The method of claim 7, wherein the first and secondregions of the first optical reflector are located within a non-centralzone of the first optical reflector.
 10. The method of claim 7, whereinrotating the first optical reflector is performed during generating thelaser beam and shooting the droplet.
 11. The method of claim 7, whereingenerating the laser and shooting the droplet are performed duringrotating the first optical reflector.
 12. The method of claim 7, furthercomprising: revolving the second optical reflector, such that the firstand second optical reflectors are rotated during generating the EUVlight in the chamber.
 13. A lithography system comprising: a collectorhaving a mirror surface and an optical axis; a laser generator aiming ata position in the optical axis and in front of the mirror surface andconfigured to generate a laser beam; a droplet generator aiming at theposition and configured to shoot at least one droplet; and a rotatableoptical reflector overlapping with the optical axis of the collector,wherein the laser generator and droplet generator are configured to haltgenerating of the laser beam and shooting the droplet after haltingrotation of the rotatable optical reflector.
 14. The lithography systemof claim 13, further comprising: a holder holding the rotatable opticalreflector; a motor; and a shaft connecting the motor and the holder. 15.The lithography system of claim 14, further comprising: a roller mountedto the holder and configured to assist with the rotation of therotatable optical reflector.
 16. The lithography system of claim 14,further comprising: a controller electrically connected to the motor,the laser generator, and the droplet generator and configured to driverotation of the rotatable optical reflector and to trigger a laseremission of the laser generator and the droplet shooting operation ofthe droplet generator.
 17. The lithography system of claim 14, furthercomprising: a first controller electrically connected to the motor andconfigured to trigger rotation of the rotatable optical reflector; and asecond controller electrically connected to the laser generator and thedroplet generator and configured to trigger laser emission of the lasergenerator and droplet shooting operation of the droplet generator. 18.The lithography system of claim 17, wherein the first controller isconfigured to trigger rotation of the rotatable optical reflector andthe second controller is configured to trigger laser emission of thelaser generator and droplet shooting operation of the droplet generatorat the same time.
 19. The lithography system of claim 17, wherein thefirst controller is configured to trigger rotation of the rotatableoptical reflector after the second controller triggers laser emission ofthe laser generator and droplet shooting operation of the dropletgenerator.
 20. The lithography system of claim 17, wherein the firstcontroller is configured to trigger rotation of the rotatable opticalreflector before the second controller triggers laser emission of thelaser generator and droplet shooting operation of the droplet generator.